Flow-through steam generator



April 28, 1970 R. MICHEL.

FLOW-THROUGH STEAM GENERATOR Filed Jan. 24, 1968 United States Patent 3,508,526 FLOW-THROUGH STEAM GENERATOR Rupprecht Michel, Erlangen, Germany, assignor to Siemens Aktiengesellschaft, Berlin, Germany, a corporation of Germany Filed Jan. 24, 1968, Ser. No. 700,163 Claims priority, application Germany, Jan. 25, 1967,

107,982 Int. Cl. F22d 7/12 US. Cl. 122-406 9 Claims ABSTRACT OF THE DISCLOSURE Flow-through steam generator includes a steam-separating vessel adapted to maintain water at a variable level therein, means for supplying a steam-water mixture to the separating vessel, the vessel having an upper space for separated steam and a lower space for separated water located at said variable level therein, evaporator means having an upstream and a downstream end, a bypass duct connecting the upper steam space of the separating vessel to a location at the downstream end of the evaporator means for passing separated steam from the separating vessel to the location, valve means connected in the by-pass duct for regulating the flow of separated steam through the by-pass duct in accordance with the level of water in the separating vessel, and means connecting the lower space of the separating vessel to the upstream end of the evaporator means for supplying water at boiling temperature to the evaporator means.

My invention relates to flow-through steam generator.

The stability of a flow-through steam generator becomes ever better with increasing enthalpy of the working medium at the inlet to the evaporator of the generator system. It is therefore expedient to introduce relatively highly preheated working medium into the evaporator. Since both the feedwater temperature and the warm-up period of the working medium in the economizer of the steam generator system is load-dependent in a steam power plant, the enthalpy of the working medium at the inlet to the vaporizer could not heretofore be raised to boiling temperature but had to maintain a margin of safety of at least 40 kcal./kg., due to the fact that it is difficult if not actually impossible to distribute or divide a steam-water mixture with adequate uniformity through the individual parallel tubes of the conventional evaporator.

It is an object of my invention to provide flow-through steam generator which avoids the aforementioned known difliculties and which, furthermore, affords the advantage derived from approaching or even exceeding the enthalpy of working medium which is beginning to vaporize when it is in the economizer or other part of the generator system located upstream of the heating surfaces or tubes located in the evaporator, without being subject to any danger of nonuniform distribution of a water-steam mixture through the parallel strings or tubes of the evaporator heating surfaces.

With the foregoing and other objects in view, I provide flow-through steam generator according to my invention comprising at least one Water-steam separating vessel, wherein a water level is maintained, connected at the upstream end of the evaporator, more particularly between a pre-evaporator having a relatively small heating surface and the main evaporator heating surface, and from the upper steam space of the separating vessel, a branching by-pass duct leads to a location at the downstream end of the evaporator, particularly at the outlet of the evaporator. A regulatable overflow or reducing Patented Apr. 28, 1970 valve is connected into the by-pass duct and permits passage therethrough of the steam separated in the separating vessel in dependence on the level of water in the separating vessel, while the water-containing lower space of the separating vessel communicates with the inlet distributor or manifold of the main evaporator.

It has been known heretofore to provide a system of radiating heating surfaces of a forced-flow steam generator formed of individual, serially connected tube packets in which the working medium is already partly evaporated and from which the steam is led away, while the water traverses the other packets. This known system, which provides steam-water separation with removal of the steam only in connection with the last or furthermost downstream tube packets of the vaporizer, is connected there, however, with the upper outlet or discharge manifolds of the individual tube packets and is furthermore structurally united therewith. Whereas, in the heretofore known system, the separated steam flows off without regulation, according to the invention of this application, the discharge of the separated steam from the separating vessel is regulated in accordance with the water level in the separating vessel. In this manner, for all operating conditions, exclusively liquid working medium is always reliably supplied to the after-connected evaporator heating surfaces or tube, whereas the steam separated in the separating vessel is first mixed with the working medium vaporized in the evaporator at a location such as the outlet of the evaporator, for example, in the flowthrough system.

In accordance with a further feature of my invention, the steam flowing from the separating vessel through the by-pass duct continuously passes through a quantity or rate-measuring device, and a regulating signal corresponding to the quantity of steam, for example, is produced for controlling the fuel-water ratio.

The features of the invention, due to their significance in increasing the stability of the evaporator heating surfaces, permit the use of a number of separate circuits which were heretofore either incapable of use or only usable with difficulty. Thus, the heating surfaces or tubes between which the separating vessel is connected, can now belong to different, separately heated boiler portions, and if desired even to separate boilers altogether.

In the case of melting chamber furnaces it has been desirable, for example, to be able to connect a heating surface initially downstream from the economizer, the heating surface forming the separating wall or partition with ash-capturing grate and for which a riser-downcomer system is desirably provided to which other piping is connected, while all the other walls of the furnace are lined or covered with piping rising upwardly with a continuous inclination or slope. It has however been difficult if not impossible heretofore to effectuate such a desirable construction, because the separating wall or partition absorbs so much heat that one must reckon with a vaporization of about 10 to 20% steam content in those heating surfaces that are located furthest upstream in the system.

Similar relationships exist in the case of a rubbish incinerator installation wherein a boiler fired by a rubbish incinerator furnace is serially connected with a conventionally fired main boiler and should cooperate therewith. Heretofore, a reduction in the rubbish incinerator firing had to be taken into account, so that for partial load of the block yet for a full accumulation of rubbish to be incinerated, steam formation in the furthermost upstream heating surfaces must be avoided. Furthermore, steam formation can now occur anywhere in the boiler portion fired by rubbish incineration without thereby impairing the stability of the water distribution over the parallel strings or tubes in the main boiler fired by coal dust, gas or oil.

The invention is also of importance for boiler installations wherein a steam-water separating vessel containing water at a given level is connected in a region between the evaporator and superheater of a flow-through system with a circulatory system superposed on the flow-through system. According to my invention, with such a vessel, a shut-off valve is connected in the vicinity of the economizer or pre-evaporator upstream of the location at which the circulatory system connects with the flowthrough system and, upstream of this shut-off valve, a by-pass duct, which is also capable of being shut off, branches off to the separating vessel. Various operational modes are thereby presented, namely, disregarding a purely conventional flow-through operation, an operation effective at start-up and at partial load with superposed circulation of a separated quantity of liquid working medium, wherein the aforementioned shut-off valve is opened while the by-pass duct is shut off. Another mode of operation provides for closing the shut-off valve and opening the hy-pass duct. A circulating pump is provided which can work in support of the light load operation selectively in series with the feedwater pump or in parallel with the evaporator.

Other features which are considered as characteristic for the invention are set forth in the appended claims.

Although the invention is illustrated and described herein as embodied in flow-through steam generator, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.

The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing, in which:

FIGS. 1 and 2 are diagrammatic circuit diagrams of two different embodiments of the flow-through steam generator according to my invention.

Referring now to the drawing, and first particularly to FIG. 1 thereof, there is shown a flow-through system having an inlet 1 for working medium drawn into the system by the feed-water pump 2. The working medium is passed through the primary heating surfaces or tubes of an economizer 3 and through the primary heating surfaces or tubes of a pre-evaporator 4 serially connected to one another. A water-steam separating vessel 6 is connected between the primary tubes of the preevaporator 4 and the main evaporator 5. A given water level 7 is maintained in the separating vessel 6. A duct 8 branches from the lower portion of the separator vessel 6 for conducting liquid working medium to the inlet distributor or manifold of the primary loop of the main evaporator 5 so that the working medium is thereby distributed over the generally parallel array of strings or heating surface members or tubes in the primary loop of the main evaporator 5. The primary loop of a pre-superheater 9 and final superheater 10 are serially connected,- in turn, to the primary loop of the main evaporator 5, downstream thereof.

A by-pass duct 11 branches off from the upper or steam chamber of the separating vessel 6 and is connected to a point between the main evaporator 5 and the pre-superheater 9. An overflow valve 12 is connected in the duct 11 and is controlled, in a conventional manner illustrated diagrammatically in FIG. 1 by the dot-dash arrow, in dependence on the water level 7, such as on its deviation from a given datum value. Furthermore, the steam discharging from the separating vessel 6 through the by-pass duct 11 is monitored by a quantity or rate measuring device such as a measuring orifice plate 21, so that the measured value can be continuously applied in the form of control signal for regulating the fuel-towater ratio of the vessel. A suitable regulating device 22 of conventional construction thus acts, as shown diagrammatically in FIG. 1 by the dotted line 23, on the feed pump 2 or a feed-water regulating valve, and as shown by the dotted line 24, on the firing system or furnace.

In the embodiment illustrated in FIG. 2 there is provided a fiow-through vessel by which a circulatory system for facilitating start-up and partial-load operation is superposed on the flow-through system of the invention. With such known flow-through vessels, a watersteam separating vessel 13 is located between the evaporator 5 and superheater 9, water in the separating vessel 13 being at a given level. A circulating pump 14 returns liquid working medium through the return duct 15 into the flow-through system at a location upstream of the pre-evaporator 5.

Elements shown in FIG. 2 which correspond or are similar to elements shown in FIG. 1 are given the same reference numerals. In applying the principle of my invention to the circuit shown in FIG. 2 or an equivalent modified circuit, the flow-through system is separable by a shutoff valve 16 connected between the pre-evaporator 4 and the main evaporator 5. A by-pass duct 17, in which another shut-otf valve 18 is connected, extends from a location just upstream of the shut-off valve 16 and connects with the water-steam separating vessel 13. The shut-off valves 16 and 18 are advantageously actuable in opposite sense of one another, i.e. when the valve 18 is closed, the valve 16 is open, and vice versa. When the valve 16 is closed and the valve 18 is open, water-steam mixture passes directly from the pre-evaporator 4 to the separating vessel 13. If desired, a valve 19 can also be provided for closing the duct connecting the evaporator 5 to the separating vessel 13 and a valve 20 between the evaporator 5 and the pre-superheater 9, the valve 20 being simultaneously kept open when the valve 19 is closed, so as to eifect thereby, during full load operation, a strict flowthrough action without any by-passes by providing a direct connection between the evaporator 5 and the pre-superheater 9, thereby avoiding unnecessary pressure losses.

As illustrated diagramatically in FIG. 2, the upstream heating surfaces of the economizer 3 and the pre-evaporator 4 can be heated by a boiler 25 fired by rubbish incineration, to produce a steam-water mixture which is then separated in the separating vessel 13 whereas the downstream heating surfaces are heated by one or more boilers 26, 27 fired by a furnace using conventional fuels such as powdered coal, oil or gas, for example.

Though not specifically shown in FIG. 2, the regulating device 22 regulates the pump 2 by conventional actuating means represented by the dotted line 23 for varying the flow of feed water into the flow-through system, and regulates a non-illustrated feeding device such as a pivoting door at the bottom of a hopper by conventional actuating means represented by the dotted line 24 for feeding garbage or the like for incineration into an appropriate furnace.

I claim:

'1. Flow-through steam generator comprising a steamwater separating vessel adapted to maintain a water level therein, means for supplying a steam-water mixture to said separating vessel, said vessel having an upper space for steam separated therein and a lower space for separated water located at a given level therein, evaporator means having an upstream and a downstream end, said upstream end of said evaporator means being downstream from said means for supplying a steam-water mixture to separating vessel, and means connecting said lower space of said separating vessel to said upstream end of said evaporator means for supplying water at boiling temperature to said evaporator means.

2. Flow-through steam generator according to claim 1 including means for measuring the quantity of steam passing through said by-pass duct and continuously applying a signal corresponding to the measured value for regulating the fuel-to-water ratio of the generator.

3. Flow-through steam generator according to claim 1 including at least one heating surface connected respectively at the upstream and downstream end of said separating vessel, said upstream and downstream heating surfaces being respectively contained in different separately heated parts of a boiler.

4. Flow-through steam generator comprising a steamwater separating vessel adapted to maintain a water level therein, at least one heating surface connected to said separating vessel upstream thereof and at least another heating surface connected to said separating vessel downstream thereof, said upstream and downstream heating surfaces being contained in respective different boilers, means for supplying a steam-water mixture to said sepa rating vessel, said vessel having an upper space for steam separated therein and a lower space for separated water located at a given level therein, evaporator means having an upstream and a downstream end, a by-pass duct connecting said upper steam space of said separating vessel to a location at the downstream end of said evaporator means for passing separated steam from said separating vessel to said location, valve means connected in said by-pass duct for regulating the flow of separated steam through said by-pass duct in accordance with the level of water in said separating vessel, and means connecting said lower space of said separating vessel to said upstream end of said evaporator means for supplying water at boiling temperature to said evaporator means.

5. Flow-through steam generator according to claim 4 in combination with a rubbish incinerating plant furnace connected with said upstream heating surface for heating the same, and a main boiler fired by a coal dust furnace associated with said downstream heating surface for heating the same.

6. Flow-through steam generator according to claim 4 in combination with a garbage incinerating plant furnace connected with said upstream heating surface for heating the same, and a main boiler fired by a gas furnace associated with said downstream heating surface for heating the same.

7. Flow-through steam generator according to claim 4 in combination with a refuse incinerating plant furnace connected with said upstream heating surface for heating the same, and a main boiler fired by an oil furnace associated with said downstream heating surface for heating the same.

8. Flow-through steam generator comprising a steamwater separating vessel adapted to maintain a water level therein, means for supplying a steam-water mixture to said separating vessel, said vessel having an upper space for steam separated therein and a lower space for separated water located at a given level therein, evaporator means having an upstream and a downstream end, a bypass duct connecting said upper steam space of said separating vessel to a location at the downstream end of said evaporator means for passing separated steam from said 6 separating vessel to said location, valve means connected in said by-pass duct for regulating the flow of separated steam through said by-pass duct in accordance with the level of water in said separating vessel, means connecting said lower space of said separating vessel to said upstream end of said evaporator means for supplying water at boiling temperature to said evaporator means, a superheater connected to said evaporator means downstream thereof, said separating vessel forming part of a circulatory system superposed on a flow-through system of the steam generator comprising a pre-evaporator, said evaporator means and said superheater serially connected in the direction of flow, said circulatory system being connected at one end to a first point located between said superheater and said evaporator means, and at the other end to a second point located between said pre-evaporator and said evaporator means, a shut-off valve connected in said flow-through system between said pre-evaporator and said second point, and another by-pass duct connecting said separating vessel to a third point located between said shut-off valve and said pre-evaporator, said other by-pass duct having means for shutting off fiow therethrough.

9. Flow-through steam generator comprising a steamwater separating vessel adapted to maintain a water level therein, means for supplying a steam-water mixture to said separating vessel, said 'vessel having an upper space for steam separated therein and a lower space for separated water located at a given level therein, evaporator means having an upstream and a downstream end, a bypass duct connecting said upper steam space of said separating vessel to a location at the downstream end of said evaporator means for passing separated steam from said separating vessel to said location, valve means connected in said by-pass duct for regulating the flow of separated steam through said by-pass duct in accordance with the level of water in said separating vessel, means connecting said lower space of said separating vessel to said upstream end of said evaporator means for supplying water at boiling temperature to said evaporator means, a superheater connected to said evaporator means downstream thereof, said separating vessel forming part of a circulatory system superposed on a flow-through system of the steam generator comprising an economizer, said evaporator means and said superheater serially connected in the direction of flow, said circulatory system being connected at one end to a first point located between said superheater and said evaporator means, and at the other end to a second point located between said economizer and said evaporator means, a first shut-off valve connected in said flow-through system between said economizer and said second point, another by-pass duct interconnecting said separating vessel and a third point located between said first shut-off valve and said economizer, and a second shut-01f valve connected in said other by-pass duct for shutting off flow therethrough.

References Cited UNITED STATES PATENTS 2,879,751 3/ 1959 Lieberherr. 2,989,038 6/ 1961 Schwarz. 3,215,126 11/1965 Sprague.

3,259,111 7/ 1966 Koch.

FOREIGN PATENTS 693,330 6/1953 Great Britain. 1,051,490 12/ 1966 Great Britain.

CHARLES J. MYHRE, Primary Examiner 

